<template>
  <ul class="list">
    <li class="item" v-for="item in letters" 
    :key="item" 
    :ref="item"
    @click="handleLetterClick"
    @touchstart.prevent="handleTouchStart"
    @touchmove="handleTouchMove"
    @touchend="handleTouchEnd"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  methods:{
    handleLetterClick(e){
      this.$emit("change",e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus =true
    },
    updated() {
      this.startY =this.$refs['A'][0].offsetTop
    },
    handleTouchMove(e){

      if(this.touchStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer =setTimeout(()=>{
      const touchY =e.touches[0].clientY-79
      const index = Math.floor((touchY-this.startY)/20)
      if(index>=0&&index<this.letters.length){
      this.$emit("change",this.letters[index])
          
        }},16)
    //  const startY =this.$refs['A'][0].offsetTop
    
      }
    },
    handleTouchEnd(){
       this.touchStatus =false
    }
  },
  computed:{
    letters(){
      const letters =[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
  data(){
  return {
    touchStatus:false,
    startY:0,
    timer:null

  }
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>